This invention relates to improved methods and apparatus for presenting a video image and the like, and more particularly relates to improved methods and apparatus for visually displaying well logging data and information.
It is well known that petroleum substances are found in subsurface earth formations, and that boreholes are conventionally drilled into such formations for the purpose of recovering these substances. What is not well known, however, is that it is conventional practice to survey the earth materials along the length of the borehole, in order to determine whether one or more of the formations traversed by the borehole contains oil or gas in commercial quantities.
More particularly, a borehole is normally logged by passing a logging tool or "sonde" through the borehole at the end of an electrically conductive logging cable which is connected at its other end to instruments at the surface. The function of the sonde is to electrically detect one or more lithological characteristics of the earth materials immediately adjacent thereto, and the function of the cable is to transmit such detections to the surface as the sonde moves through the borehole. Accordingly, the surface instrumentation will conventionally include provision for indicating the depth of the sonde in the borehole in correlation with receipt of the signals from the sonde, as well as provision for processing and recording such signals.
It is seldom that a single well logging measurement will provide sufficient basis for a conclusive determination as to the presence of petroleum substances in a particular formation of interest. Accordingly, it is essential that the resulting measurement be registered in a permanent manner whereby it can be studied, and whereby all or portions of the measurement may be compared or correlated with other lithological data. Accordingly, various recording devices such as a pentype chart recorder or a camera have been developed and used for these purposes.
It is also desirable for the well logging system to include means for observing and monitoring the logging measurement as it is being derived from the sonde, inasmuch as this permits the logging operator to adjust and control the system to provide the most accurate and meaningful measurement. The conventional chart-type recorder is particularly desirable in this respect, since the paper chart is easily visible to the operator as the pen moves to draw the log. On the other hand, the resulting paper chart cannot be adjusted once it is produced, nor can the recorder inscribe supplemental data on the chart. Furthermore, duplicates of the measurement cannot be conveniently obtained for correlation with other data, except by tracing the graph onto another sheet of paper or the like.
The camera recorder, which employs a beam of light which moves appropriately across a strip of photographic film, produces a record which can be easily duplicated. However, the strip of film is relatively inaccessible during the logging operation, and therefore does not permit the measurement to be conveniently observed during the course of the logging measurement.
Recently, improved well logging systems and techniques have been developed such as those described in U.S. patent application Ser. No. 949,592, which was filed Oct. 10, 1978, wherein the logging measurements are derived in or converted from analog to digital form, and wherein these measurements may be conveniently recorded using magnetic tape. Although this improvement has provided for easy reproduction of an unlimited number of copies of all or any portion of the measurement, and although this has further permitted the measurement to be easily and conveniently correlated and even combined with other lithological data, the magnetic tape does not itself provide for visible observation of the logging data being stored on the tape as such. Accordingly, it is desirable to include a video-type capability in the logging system whereby the logging measurement may be conveniently observed and monitored by the operator as it is derived from the borehole, and whereby the operator may conveniently control and adjust the system and even portions of the measurements as they are generated.
The video capability includes a cathode ray tube or the like, wherein the screen presents a visible image of at least the most recent 100 feet or other preselected portion of the measurement along the "curve", and also together with a further array of horizontal lines to indicate the depth in the borehole at points along the curve. Thus, the logging measurement will appear as a representation which progresses vertically across the video screen to illustrate passage of the sonde along the borehole between the depths indicated by the horizontal lines on the screen, and the relative horizontal displacement of the curve with respect to the vertical lines on the screen serve to indicate the magnitude of the lithological parameter being derived.
As more effective methods are discovered for deriving a plurality of different measurements during the same logging "trip" through the borehole, thus the need to observe these measurements as they are derived and magnetically recorded in a correlative manner is even more important for the reasons hereinbefore set forth. Moreover, the advent of logging systems wherein the measurements are recorded on magnetic tape, has enhanced the need for a video capability to display these measurements to the operator in the most meaningful manner.
It will be apparent that a video capability that will not only accumulate and present an image representing a full preselected segment of the logging measurement, but which will further scroll the image in correlation with travel of the sonde to continually present a full preselected portion of the measurement at all times, would be far more useful to the operator. If it is assumed that the video screen is composed of an array of 400 lines, each line in turn being composed of 512 points or "stations", however, it will also be readily apparent that this, in turn, would call for a memory capability sufficient to store a total of 204,800 "X-Y" coordinates. More important, it would require a scanning and selection capability which would continually recall and display each of these coordinates at a rate which would be fast enough to avoid producing a flickering image on the video screen.
These disadvantages are overcome with the present invention, however, and novel video display means and method are provided for presenting a scrolling image which is not only continually representative of a full preselected length of logging measurement, but which also eliminates the need for elaborate and high-speed storage, or storage-type oscilloscopes and the like to avoid flicker.